The present invention relates in general to low frequency wide band signal couplers. More particularly, the invention herein discloses a low frequency wide band multi-directional tap circuit, and in another embodiment a low frequency, wide band multi-directional signal splitter. These circuits have use in CATV and related applications.
Presently, for CATV applications coupler devices are used for interconnecting a main signal line with a subscriber. However, such devices have directionality limitations and generally only permit signal communication from a central control unit to the subscriber.
Accordingly, it is an object of the present invention to provide a signal coupler preferably for CATV applications and wherein signal communication is permitted in multiple directions with no such directionality limitation referred to hereinbefore. In this way communication can occur, not only from the central unit to the subscriber, but also between subscribers. In this regard it is understood that the subscriber can take on many forms including a work station, word processor, or even some form of mechanical robot that is to be controlled.
Previously, conventional resistive directional couplers might have been contemplated for such applications. However, these devices are too lossy.
Accordingly, another object of the present invention is to provide an improved low frequency wide band coupler that has low through loss and also that is matched. The signal coupler of the present invention is usable at frequency ranges of 1 KHz to 900 MHz, however, the preferred operating range is 0.01-5.0 MHz.
A further object of the present invention is to provide a low frequency wide band multi-directional signal coupler that is of extremely simple construction, that has very good electrical characteristics, and that can be manufactured relatively inexpensively.
Still another object of the present invention is to provide a low frequency wide band signal coupler that may be embodied either as a tap circuit or as a signal splitter both versions of which exhibit multi-directional signal characteristics.
To accomplish the foregoing and other objects of this invention there is provided a low frequency, wide band signal coupler which is described herein in two different versions. In accordance with one version of the present invention, this is meant for connection from a main communication line to a subscriber. The second version may be more appropriately identified as a signal splitter for splitting a signal from a main line to separate lines to be coupled to two separate groups of subscribers. In accordance with the first embodiment of the invention the coupler comprises an input terminal for receiving an input signal which is in the frequency range of 1 KHz to 900 MHz, and an output terminal. Conductive electrical means intercouple the input and output terminals enabling signal coupling from the input to the output. The signal coupler also comprises an inductive winding having N turns and coupled from the conductive electrical means. There is also provided a tap output terminal. This signal coupler may be referred to as a tap or tap circuit. Finally, there is provided a signal tap node from the inductive winding taken at a location along the winding separating the N turn winding into n.sub.1 and n.sub.2 turns where n.sub.1 /n.sub.2 is greater than zero. Means intercouple the signal tap node and the tap output terminal including a resistor means. In the disclosed embodiment this resistor is a 62 ohm resistor. The conductive electrical means may comprise a direct wire connection between input and output terminals. There is also preferably provided a core upon which the winding is wound. This device is particularly meant for use with coax cable input and output connections.
In accordance with the other version of the present invention which is in the form of a signal splitter, this low frequency, wide band device comprises an input terminal for receiving an input signal in the frequency range of 1 KHz to 900 MHz. More particularly the frequency range may be 0.01-5.0 MHz. The coupler also includes a first output terminal and a second output terminal. The signal at the input terminal splits to the two output terminals. The circuit includes three transformers each having a pair of windings including a first and a second winding. Means couple the input and first and second output terminals to first windings of the respective three transformers. Means also couple the three second windings in a series circuit. Also included are three isolation resistors and means coupling the isolation resistors each respectively across one of the second windings. Each of the transformers preferably comprise a core upon which the pair of windings is wound. There is also included conductive electrical means intercoupling the first and second windings of each transformer at an intermediate point of their ends. The isolation resistors are preferably of a value on the order of twice the coaxial cable impedance. These resistors in the disclosed embodiment are in the range of 130-150 ohms.